Problem: Determine how many solutions exist for the system of equations. ${4x+y = -1}$ ${y = -7-6x}$
Answer: Convert both equations to slope-intercept form: ${4x+y = -1}$ $4x{-4x} + y = -1{-4x}$ $y = -1-4x$ ${y = -4x-1}$ ${y = -7-6x}$ ${y = -6x-7}$ Just by looking at both equations in slope-intercept form, what can you determine? ${y = -4x-1}$ ${y = -6x-7}$ The linear equations have different slopes. ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ When two equations have different slopes, the lines will intersect once with one solution.